Date.prototype.defaultFormat = function () {
  return this.format("yyyy-MM-dd");
};
Date.prototype.format = function (format) {
  let date = {
      "M+": this.getMonth() + 1,
      "d+": this.getDate(),
      "h+": this.getHours(),
      "m+": this.getMinutes(),
      "s+": this.getSeconds(),
      "q+": Math.floor((this.getMonth() + 3) / 3),
      "S+": this.getMilliseconds()
  };
  if (/(y+)/i.test(format)) {
      format = format.replace(RegExp.$1, (this.getFullYear() + '').substr(4 - RegExp.$1.length));
  }
  for (let k in date) {
      if (new RegExp("(" + k + ")").test(format)) {
          format = format.replace(RegExp.$1, RegExp.$1.length == 1
              ? date[k] : ("00" + date[k]).substr(("" + date[k]).length));
      }
  }
  return format;
};